<!DOCTYPE html>
<html lang="en-US">
  <head>
    <meta charset="utf-8">
    <meta name="viewport" content="width=device-width,initial-scale=1">
    <title>Key的理解 | 前端档案</title>
    <meta name="generator" content="VuePress 1.8.2">
    <link rel="icon" href="/favicon.ico">
    <meta name="description" content="前端通关宝典">
    <meta name="theme-color" content="#3eaf7c">
    <meta name="apple-mobile-web-app-capable" content="yes">
    <meta name="apple-mobile-web-app-status-bar-style" content="black">
    
    <link rel="preload" href="/assets/css/0.styles.e02fc531.css" as="style"><link rel="preload" href="/assets/js/app.bf44e39b.js" as="script"><link rel="preload" href="/assets/js/2.db7a59af.js" as="script"><link rel="preload" href="/assets/js/222.51d8a12c.js" as="script"><link rel="prefetch" href="/assets/js/10.3bbe2f24.js"><link rel="prefetch" href="/assets/js/100.43061c81.js"><link rel="prefetch" href="/assets/js/101.2e8a188c.js"><link rel="prefetch" href="/assets/js/102.3f4f14f0.js"><link rel="prefetch" href="/assets/js/103.5ed45f48.js"><link rel="prefetch" href="/assets/js/104.29ef9283.js"><link rel="prefetch" href="/assets/js/105.e4051d70.js"><link rel="prefetch" href="/assets/js/106.ec073f00.js"><link rel="prefetch" href="/assets/js/107.9b165150.js"><link rel="prefetch" href="/assets/js/108.c0031864.js"><link rel="prefetch" href="/assets/js/109.06bb75a7.js"><link rel="prefetch" href="/assets/js/11.402e3434.js"><link rel="prefetch" href="/assets/js/110.edc92528.js"><link rel="prefetch" href="/assets/js/111.e50e0cca.js"><link rel="prefetch" href="/assets/js/112.b0decdf4.js"><link rel="prefetch" href="/assets/js/113.f0801886.js"><link rel="prefetch" href="/assets/js/114.25ab8fa4.js"><link rel="prefetch" href="/assets/js/115.36fc62f3.js"><link rel="prefetch" href="/assets/js/116.8df9a6aa.js"><link rel="prefetch" href="/assets/js/117.1ec0fada.js"><link rel="prefetch" href="/assets/js/118.51c54869.js"><link rel="prefetch" href="/assets/js/119.d708669d.js"><link rel="prefetch" href="/assets/js/12.eba9a66a.js"><link rel="prefetch" href="/assets/js/120.a44efeea.js"><link rel="prefetch" href="/assets/js/121.581a4ae4.js"><link rel="prefetch" href="/assets/js/122.e54e19e1.js"><link rel="prefetch" href="/assets/js/123.62aa41d0.js"><link rel="prefetch" href="/assets/js/124.c51c6b7f.js"><link rel="prefetch" href="/assets/js/125.68055811.js"><link rel="prefetch" href="/assets/js/126.8b16d246.js"><link rel="prefetch" href="/assets/js/127.fc7608d6.js"><link rel="prefetch" href="/assets/js/128.0df431fc.js"><link rel="prefetch" href="/assets/js/129.77241cfd.js"><link rel="prefetch" href="/assets/js/13.a3e65817.js"><link rel="prefetch" href="/assets/js/130.2bf0b622.js"><link rel="prefetch" href="/assets/js/131.77da1093.js"><link rel="prefetch" href="/assets/js/132.c1ac84bc.js"><link rel="prefetch" href="/assets/js/133.001af559.js"><link rel="prefetch" href="/assets/js/134.98ff69db.js"><link rel="prefetch" href="/assets/js/135.b91963f4.js"><link rel="prefetch" href="/assets/js/136.e3df531a.js"><link rel="prefetch" href="/assets/js/137.157c5a5f.js"><link rel="prefetch" href="/assets/js/138.1d3a1791.js"><link rel="prefetch" href="/assets/js/139.9e17df54.js"><link rel="prefetch" href="/assets/js/14.bd9cc5f8.js"><link rel="prefetch" href="/assets/js/140.22839840.js"><link rel="prefetch" href="/assets/js/141.dbde614d.js"><link rel="prefetch" href="/assets/js/142.5a6858ba.js"><link rel="prefetch" href="/assets/js/143.e26d707c.js"><link rel="prefetch" href="/assets/js/144.5b1fbe13.js"><link rel="prefetch" href="/assets/js/145.09921e20.js"><link rel="prefetch" href="/assets/js/146.8ea606b7.js"><link rel="prefetch" href="/assets/js/147.41bda9d5.js"><link rel="prefetch" href="/assets/js/148.d89f18bc.js"><link rel="prefetch" href="/assets/js/149.16aa39c9.js"><link rel="prefetch" href="/assets/js/15.deb2f25a.js"><link rel="prefetch" href="/assets/js/150.07798494.js"><link rel="prefetch" href="/assets/js/151.6732ee94.js"><link rel="prefetch" href="/assets/js/152.c644167e.js"><link rel="prefetch" href="/assets/js/153.040f256b.js"><link rel="prefetch" href="/assets/js/154.1cec3035.js"><link rel="prefetch" href="/assets/js/155.a4b51a17.js"><link rel="prefetch" href="/assets/js/156.095b78e0.js"><link rel="prefetch" href="/assets/js/157.eb262a26.js"><link rel="prefetch" href="/assets/js/158.35756e8c.js"><link rel="prefetch" href="/assets/js/159.6ac43664.js"><link rel="prefetch" href="/assets/js/16.c7b17381.js"><link rel="prefetch" href="/assets/js/160.0a56c40c.js"><link rel="prefetch" href="/assets/js/161.8320b48a.js"><link rel="prefetch" href="/assets/js/162.09ba1172.js"><link rel="prefetch" href="/assets/js/163.f7fb82e8.js"><link rel="prefetch" href="/assets/js/164.ab9df42b.js"><link rel="prefetch" href="/assets/js/165.f012858f.js"><link rel="prefetch" href="/assets/js/166.b3f190e3.js"><link rel="prefetch" href="/assets/js/167.43b66e59.js"><link rel="prefetch" href="/assets/js/168.4eb162d3.js"><link rel="prefetch" href="/assets/js/169.0375d2cf.js"><link rel="prefetch" href="/assets/js/17.da61c942.js"><link rel="prefetch" href="/assets/js/170.90c9c235.js"><link rel="prefetch" href="/assets/js/171.672fc257.js"><link rel="prefetch" href="/assets/js/172.dfa9d8d9.js"><link rel="prefetch" href="/assets/js/173.61a6ec8e.js"><link rel="prefetch" href="/assets/js/174.4f4ef0d7.js"><link rel="prefetch" href="/assets/js/175.675d01d1.js"><link rel="prefetch" href="/assets/js/176.5bd1bcb7.js"><link rel="prefetch" href="/assets/js/177.4355dadd.js"><link rel="prefetch" href="/assets/js/178.79ed29b8.js"><link rel="prefetch" href="/assets/js/179.2247dc30.js"><link rel="prefetch" href="/assets/js/18.6e554767.js"><link rel="prefetch" href="/assets/js/180.db79361a.js"><link rel="prefetch" href="/assets/js/181.85a33295.js"><link rel="prefetch" href="/assets/js/182.0bc317bc.js"><link rel="prefetch" href="/assets/js/183.7769a38e.js"><link rel="prefetch" href="/assets/js/184.9b0aba05.js"><link rel="prefetch" href="/assets/js/185.f6dc87bd.js"><link rel="prefetch" href="/assets/js/186.e3b7de00.js"><link rel="prefetch" href="/assets/js/187.a6dadcea.js"><link rel="prefetch" href="/assets/js/188.d3f8b0e3.js"><link rel="prefetch" href="/assets/js/189.1112499f.js"><link rel="prefetch" href="/assets/js/19.f800e0d1.js"><link rel="prefetch" href="/assets/js/190.e3255e84.js"><link rel="prefetch" href="/assets/js/191.34deece6.js"><link rel="prefetch" href="/assets/js/192.69821c0e.js"><link rel="prefetch" href="/assets/js/193.769a5088.js"><link rel="prefetch" href="/assets/js/194.afaa2cde.js"><link rel="prefetch" href="/assets/js/195.5b94bbc6.js"><link rel="prefetch" href="/assets/js/196.3b078264.js"><link rel="prefetch" href="/assets/js/197.2d9585d3.js"><link rel="prefetch" href="/assets/js/198.3095d8b8.js"><link rel="prefetch" href="/assets/js/199.79b6db11.js"><link rel="prefetch" href="/assets/js/20.4a74a968.js"><link rel="prefetch" href="/assets/js/200.c309ef7a.js"><link rel="prefetch" href="/assets/js/201.bded46e8.js"><link rel="prefetch" href="/assets/js/202.801fb3ea.js"><link rel="prefetch" href="/assets/js/203.b9933f5e.js"><link rel="prefetch" href="/assets/js/204.255b43df.js"><link rel="prefetch" href="/assets/js/205.000fb7ac.js"><link rel="prefetch" href="/assets/js/206.8f945829.js"><link rel="prefetch" href="/assets/js/207.74942b2e.js"><link rel="prefetch" href="/assets/js/208.329d8230.js"><link rel="prefetch" href="/assets/js/209.3fc54586.js"><link rel="prefetch" href="/assets/js/21.5f725cbd.js"><link rel="prefetch" href="/assets/js/210.1aa9659f.js"><link rel="prefetch" href="/assets/js/211.702df03f.js"><link rel="prefetch" href="/assets/js/212.ca95f208.js"><link rel="prefetch" href="/assets/js/213.024b4fa6.js"><link rel="prefetch" href="/assets/js/214.e2830dd8.js"><link rel="prefetch" href="/assets/js/215.0b646cb4.js"><link rel="prefetch" href="/assets/js/216.9bd6d019.js"><link rel="prefetch" href="/assets/js/217.586593b4.js"><link rel="prefetch" href="/assets/js/218.a2244829.js"><link rel="prefetch" href="/assets/js/219.1d858220.js"><link rel="prefetch" href="/assets/js/22.7d2b7a74.js"><link rel="prefetch" href="/assets/js/220.7f5e3dbd.js"><link rel="prefetch" href="/assets/js/221.d1f79d31.js"><link rel="prefetch" href="/assets/js/223.797028ea.js"><link rel="prefetch" href="/assets/js/224.d925bf8b.js"><link rel="prefetch" href="/assets/js/225.cfe12606.js"><link rel="prefetch" href="/assets/js/226.b6bd41b4.js"><link rel="prefetch" href="/assets/js/227.15412d16.js"><link rel="prefetch" href="/assets/js/228.66af5157.js"><link rel="prefetch" href="/assets/js/229.cfb11559.js"><link rel="prefetch" href="/assets/js/23.1409c9f4.js"><link rel="prefetch" href="/assets/js/230.d2e613b5.js"><link rel="prefetch" href="/assets/js/231.85b8958b.js"><link rel="prefetch" href="/assets/js/232.42df48c8.js"><link rel="prefetch" href="/assets/js/233.d3be0c78.js"><link rel="prefetch" href="/assets/js/234.bb68d0be.js"><link rel="prefetch" href="/assets/js/235.bfd00052.js"><link rel="prefetch" href="/assets/js/236.3d58cc9d.js"><link rel="prefetch" href="/assets/js/237.d9af6062.js"><link rel="prefetch" href="/assets/js/238.54894974.js"><link rel="prefetch" href="/assets/js/239.b69669d0.js"><link rel="prefetch" href="/assets/js/24.e06b2b32.js"><link rel="prefetch" href="/assets/js/240.44f7b333.js"><link rel="prefetch" href="/assets/js/241.2d307b1a.js"><link rel="prefetch" href="/assets/js/242.47aecf42.js"><link rel="prefetch" href="/assets/js/243.b5afbb6e.js"><link rel="prefetch" href="/assets/js/244.8e04094f.js"><link rel="prefetch" href="/assets/js/245.78009475.js"><link rel="prefetch" href="/assets/js/246.eb7991c2.js"><link rel="prefetch" href="/assets/js/247.00c024fd.js"><link rel="prefetch" href="/assets/js/248.144c2842.js"><link rel="prefetch" href="/assets/js/249.35bae652.js"><link rel="prefetch" href="/assets/js/25.5e7aeaa8.js"><link rel="prefetch" href="/assets/js/250.854bde18.js"><link rel="prefetch" href="/assets/js/251.7cbb77f8.js"><link rel="prefetch" href="/assets/js/252.1ed96448.js"><link rel="prefetch" href="/assets/js/253.9d736b7d.js"><link rel="prefetch" href="/assets/js/254.137c6595.js"><link rel="prefetch" href="/assets/js/255.ac6865dc.js"><link rel="prefetch" href="/assets/js/256.055e06fd.js"><link rel="prefetch" href="/assets/js/257.63559614.js"><link rel="prefetch" href="/assets/js/258.b6958ba1.js"><link rel="prefetch" href="/assets/js/259.bc6da491.js"><link rel="prefetch" href="/assets/js/26.77d42111.js"><link rel="prefetch" href="/assets/js/260.a8e9559d.js"><link rel="prefetch" href="/assets/js/261.b051c6dd.js"><link rel="prefetch" href="/assets/js/262.e83c7ca8.js"><link rel="prefetch" href="/assets/js/263.bd14a165.js"><link rel="prefetch" href="/assets/js/264.65c3b624.js"><link rel="prefetch" href="/assets/js/265.db4371b9.js"><link rel="prefetch" href="/assets/js/266.97118d6c.js"><link rel="prefetch" href="/assets/js/267.de83cb0b.js"><link rel="prefetch" href="/assets/js/268.2bdd86cb.js"><link rel="prefetch" href="/assets/js/269.9c9a802f.js"><link rel="prefetch" href="/assets/js/27.fa37605f.js"><link rel="prefetch" href="/assets/js/270.f599f9fe.js"><link rel="prefetch" href="/assets/js/271.275d4619.js"><link rel="prefetch" href="/assets/js/272.ed0fabf6.js"><link rel="prefetch" href="/assets/js/273.fc279fbe.js"><link rel="prefetch" href="/assets/js/274.fe4b3d21.js"><link rel="prefetch" href="/assets/js/275.922677e1.js"><link rel="prefetch" href="/assets/js/276.597ceb81.js"><link rel="prefetch" href="/assets/js/277.71871d2e.js"><link rel="prefetch" href="/assets/js/278.10923657.js"><link rel="prefetch" href="/assets/js/279.cddbf2d7.js"><link rel="prefetch" href="/assets/js/28.7418a003.js"><link rel="prefetch" href="/assets/js/280.66542c64.js"><link rel="prefetch" href="/assets/js/281.c7ca5292.js"><link rel="prefetch" href="/assets/js/282.d105ef08.js"><link rel="prefetch" href="/assets/js/283.ae8d69c7.js"><link rel="prefetch" href="/assets/js/284.8763c337.js"><link rel="prefetch" href="/assets/js/285.cce4e007.js"><link rel="prefetch" href="/assets/js/29.42b5bf54.js"><link rel="prefetch" href="/assets/js/3.a2af090e.js"><link rel="prefetch" href="/assets/js/30.7fe0ece5.js"><link rel="prefetch" href="/assets/js/31.e05d012e.js"><link rel="prefetch" href="/assets/js/32.0a6466c6.js"><link rel="prefetch" href="/assets/js/33.8db270b1.js"><link rel="prefetch" href="/assets/js/34.c6e6ae70.js"><link rel="prefetch" href="/assets/js/35.8fc12d56.js"><link rel="prefetch" href="/assets/js/36.cb54baf3.js"><link rel="prefetch" href="/assets/js/37.656cb8eb.js"><link rel="prefetch" href="/assets/js/38.9152ff6b.js"><link rel="prefetch" href="/assets/js/39.f71e5e3d.js"><link rel="prefetch" href="/assets/js/4.02de3c47.js"><link rel="prefetch" href="/assets/js/40.3d664ab4.js"><link rel="prefetch" href="/assets/js/41.fc6e4f78.js"><link rel="prefetch" href="/assets/js/42.c17c3353.js"><link rel="prefetch" href="/assets/js/43.e78a329f.js"><link rel="prefetch" href="/assets/js/44.326a0948.js"><link rel="prefetch" href="/assets/js/45.67e6e1d4.js"><link rel="prefetch" href="/assets/js/46.85f71b1e.js"><link rel="prefetch" href="/assets/js/47.f2e524a6.js"><link rel="prefetch" href="/assets/js/48.843108ee.js"><link rel="prefetch" href="/assets/js/49.98713c95.js"><link rel="prefetch" href="/assets/js/5.f38c3daa.js"><link rel="prefetch" href="/assets/js/50.2c70898f.js"><link rel="prefetch" href="/assets/js/51.023fea5d.js"><link rel="prefetch" href="/assets/js/52.3877af4c.js"><link rel="prefetch" href="/assets/js/53.3938d117.js"><link rel="prefetch" href="/assets/js/54.4cf45721.js"><link rel="prefetch" href="/assets/js/55.6894de94.js"><link rel="prefetch" href="/assets/js/56.48fd0f63.js"><link rel="prefetch" href="/assets/js/57.2c3b8155.js"><link rel="prefetch" href="/assets/js/58.fee976b4.js"><link rel="prefetch" href="/assets/js/59.d57c3ac9.js"><link rel="prefetch" href="/assets/js/6.a7d50f34.js"><link rel="prefetch" href="/assets/js/60.9954df49.js"><link rel="prefetch" href="/assets/js/61.1b870f60.js"><link rel="prefetch" href="/assets/js/62.37537ac3.js"><link rel="prefetch" href="/assets/js/63.5e7cfac8.js"><link rel="prefetch" href="/assets/js/64.407003ca.js"><link rel="prefetch" href="/assets/js/65.ba6c5d7d.js"><link rel="prefetch" href="/assets/js/66.2b5a751b.js"><link rel="prefetch" href="/assets/js/67.2faf15d0.js"><link rel="prefetch" href="/assets/js/68.19e50dcb.js"><link rel="prefetch" href="/assets/js/69.eec003cb.js"><link rel="prefetch" href="/assets/js/7.6c196c91.js"><link rel="prefetch" href="/assets/js/70.98d2461a.js"><link rel="prefetch" href="/assets/js/71.184225a4.js"><link rel="prefetch" href="/assets/js/72.956d136a.js"><link rel="prefetch" href="/assets/js/73.3e68378e.js"><link rel="prefetch" href="/assets/js/74.cec669e7.js"><link rel="prefetch" href="/assets/js/75.d418b5f0.js"><link rel="prefetch" href="/assets/js/76.f3f9ccd6.js"><link rel="prefetch" href="/assets/js/77.f24df03b.js"><link rel="prefetch" href="/assets/js/78.7eee67a8.js"><link rel="prefetch" href="/assets/js/79.8fadb3f7.js"><link rel="prefetch" href="/assets/js/8.b7eb2fb2.js"><link rel="prefetch" href="/assets/js/80.4f6165b0.js"><link rel="prefetch" href="/assets/js/81.49b03807.js"><link rel="prefetch" href="/assets/js/82.7ea07224.js"><link rel="prefetch" href="/assets/js/83.d6bd71b7.js"><link rel="prefetch" href="/assets/js/84.26db1aa8.js"><link rel="prefetch" href="/assets/js/85.c8f1f3bb.js"><link rel="prefetch" href="/assets/js/86.fd1c3c7f.js"><link rel="prefetch" href="/assets/js/87.38ab6ed9.js"><link rel="prefetch" href="/assets/js/88.f0a874e0.js"><link rel="prefetch" href="/assets/js/89.2b3352d4.js"><link rel="prefetch" href="/assets/js/9.d7ae4925.js"><link rel="prefetch" href="/assets/js/90.286cc7d4.js"><link rel="prefetch" href="/assets/js/91.c17c366b.js"><link rel="prefetch" href="/assets/js/92.29bc2389.js"><link rel="prefetch" href="/assets/js/93.6d335097.js"><link rel="prefetch" href="/assets/js/94.89ab26c7.js"><link rel="prefetch" href="/assets/js/95.f2493183.js"><link rel="prefetch" href="/assets/js/96.6662ec36.js"><link rel="prefetch" href="/assets/js/97.22c9d3f9.js"><link rel="prefetch" href="/assets/js/98.0b0b77a2.js"><link rel="prefetch" href="/assets/js/99.df5f5981.js">
    <link rel="stylesheet" href="/assets/css/0.styles.e02fc531.css">
  </head>
  <body>
    <div id="app" data-server-rendered="true"><div class="theme-container"><header class="navbar"><div class="sidebar-button"><svg xmlns="http://www.w3.org/2000/svg" aria-hidden="true" role="img" viewBox="0 0 448 512" class="icon"><path fill="currentColor" d="M436 124H12c-6.627 0-12-5.373-12-12V80c0-6.627 5.373-12 12-12h424c6.627 0 12 5.373 12 12v32c0 6.627-5.373 12-12 12zm0 160H12c-6.627 0-12-5.373-12-12v-32c0-6.627 5.373-12 12-12h424c6.627 0 12 5.373 12 12v32c0 6.627-5.373 12-12 12zm0 160H12c-6.627 0-12-5.373-12-12v-32c0-6.627 5.373-12 12-12h424c6.627 0 12 5.373 12 12v32c0 6.627-5.373 12-12 12z"></path></svg></div> <a href="/" class="home-link router-link-active"><img src="/images/logo.png" alt="前端档案" class="logo"> <span class="site-name can-hide">前端档案</span></a> <div class="links"><div class="search-box"><input aria-label="Search" autocomplete="off" spellcheck="false" value=""> <!----></div> <nav class="nav-links can-hide"><div class="nav-item"><a href="/guide/" class="nav-link">
  指南
</a></div><div class="nav-item"><a href="/fe/" class="nav-link router-link-active">
  前端
</a></div><div class="nav-item"><a href="/be/" class="nav-link">
  后端
</a></div><div class="nav-item"><a href="/base/" class="nav-link">
  基础
</a></div><div class="nav-item"><a href="/tools/" class="nav-link">
  工具
</a></div><div class="nav-item"><a href="/resume/" class="nav-link">
  简历
</a></div><div class="nav-item"><a href="/experience/" class="nav-link">
  面经
</a></div><div class="nav-item"><a href="/technology/" class="nav-link">
  八股文
</a></div><div class="nav-item"><a href="/thinks/" class="nav-link">
  思考
</a></div> <!----></nav></div></header> <div class="sidebar-mask"></div> <aside class="sidebar"><nav class="nav-links"><div class="nav-item"><a href="/guide/" class="nav-link">
  指南
</a></div><div class="nav-item"><a href="/fe/" class="nav-link router-link-active">
  前端
</a></div><div class="nav-item"><a href="/be/" class="nav-link">
  后端
</a></div><div class="nav-item"><a href="/base/" class="nav-link">
  基础
</a></div><div class="nav-item"><a href="/tools/" class="nav-link">
  工具
</a></div><div class="nav-item"><a href="/resume/" class="nav-link">
  简历
</a></div><div class="nav-item"><a href="/experience/" class="nav-link">
  面经
</a></div><div class="nav-item"><a href="/technology/" class="nav-link">
  八股文
</a></div><div class="nav-item"><a href="/thinks/" class="nav-link">
  思考
</a></div> <!----></nav>  <ul class="sidebar-links"><li><a href="/fe/" aria-current="page" class="sidebar-link">大前端学习路径 + B站资源整合</a></li><li><section class="sidebar-group collapsable depth-0"><p class="sidebar-heading"><span>HTML</span> <span class="arrow right"></span></p> <!----></section></li><li><section class="sidebar-group collapsable depth-0"><p class="sidebar-heading"><span>CSS</span> <span class="arrow right"></span></p> <!----></section></li><li><section class="sidebar-group collapsable depth-0"><p class="sidebar-heading"><span>JavaScript</span> <span class="arrow right"></span></p> <!----></section></li><li><section class="sidebar-group collapsable depth-0"><p class="sidebar-heading"><span>TypeScript</span> <span class="arrow right"></span></p> <!----></section></li><li><section class="sidebar-group collapsable depth-0"><p class="sidebar-heading"><span>ES6</span> <span class="arrow right"></span></p> <!----></section></li><li><section class="sidebar-group collapsable depth-0"><p class="sidebar-heading open"><span>Vue</span> <span class="arrow down"></span></p> <ul class="sidebar-links sidebar-group-items"><li><a href="/fe/vue/" aria-current="page" class="sidebar-link">Vue的理解</a></li><li><a href="/fe/vue/mvvm.html" class="sidebar-link">MVVM 双向数据绑定</a></li><li><a href="/fe/vue/spa.html" class="sidebar-link">面试官：你对SPA单页面的理解，它的优缺点分别是什么？如何实现SPA应用呢</a></li><li><a href="/fe/vue/show_if.html" class="sidebar-link">v-show 和 v-if 有什么区别？</a></li><li><a href="/fe/vue/new_vue.html" class="sidebar-link">面试官：Vue实例挂载的过程</a></li><li><a href="/fe/vue/lifecycle.html" class="sidebar-link">面试官：请描述下你对vue生命周期的理解？在created和mounted这两个生命周期中请求数据有什么区别呢？</a></li><li><a href="/fe/vue/if_for.html" class="sidebar-link">面试官：v-if和v-for的优先级是什么？</a></li><li><a href="/fe/vue/computed_watch.html" class="sidebar-link">计算属性 VS 监听属性</a></li><li><a href="/fe/vue/first_page_time.html" class="sidebar-link">面试官：SPA首屏加载速度慢的怎么解决？</a></li><li><a href="/fe/vue/data.html" class="sidebar-link">面试官：为什么data属性是一个函数而不是一个对象？</a></li><li><a href="/fe/vue/data_object_add_attrs.html" class="sidebar-link">面试官：动态给vue的data添加一个新的属性时会发生什么？怎样解决？</a></li><li><a href="/fe/vue/components_plugin.html" class="sidebar-link">面试官：Vue中组件和插件有什么区别？</a></li><li><a href="/fe/vue/communication.html" class="sidebar-link">面试官：Vue组件之间的通信方式都有哪些？</a></li><li><a href="/fe/vue/nexttick.html" class="sidebar-link">面试官：Vue中的$nextTick有什么作用？</a></li><li><a href="/fe/vue/mixin.html" class="sidebar-link">Mixin 混入</a></li><li><a href="/fe/vue/slot.html" class="sidebar-link">面试官：说说你对slot的理解？slot使用场景有哪些？</a></li><li><a href="/fe/vue/observable.html" class="sidebar-link">面试官：Vue.observable你有了解过吗？说说看</a></li><li><a href="/fe/vue/key.html" aria-current="page" class="active sidebar-link">Key的理解</a><ul class="sidebar-sub-headers"><li class="sidebar-sub-header"><a href="/fe/vue/key.html#一、key是什么" class="sidebar-link">一、Key是什么</a></li><li class="sidebar-sub-header"><a href="/fe/vue/key.html#二、设置key与不设置key区别" class="sidebar-link">二、设置key与不设置key区别</a></li><li class="sidebar-sub-header"><a href="/fe/vue/key.html#三、原理分析" class="sidebar-link">三、原理分析</a></li><li class="sidebar-sub-header"><a href="/fe/vue/key.html#参考文献" class="sidebar-link">参考文献</a></li></ul></li><li><a href="/fe/vue/keepalive.html" class="sidebar-link">面试官：说说你对keep-alive的理解是什么？</a></li><li><a href="/fe/vue/modifier.html" class="sidebar-link">面试官：Vue常用的修饰符有哪些有什么应用场景</a></li><li><a href="/fe/vue/directive.html" class="sidebar-link">面试官：你有写过自定义指令吗？自定义指令的应用场景有哪些？</a></li><li><a href="/fe/vue/filter.html" class="sidebar-link">面试官：Vue中的过滤器了解吗？过滤器的应用场景有哪些？</a></li><li><a href="/fe/vue/vnode.html" class="sidebar-link">虚拟DOM</a></li><li><a href="/fe/vue/diff.html" class="sidebar-link">Diff 算法</a></li><li><a href="/fe/vue/axios.html" class="sidebar-link">面试官：Vue项目中有封装过axios吗？主要是封装哪方面的？</a></li><li><a href="/fe/vue/axios_code.html" class="sidebar-link">面试官：你了解axios的原理吗？有看过它的源码吗？</a></li><li><a href="/fe/vue/ssr.html" class="sidebar-link">面试官：SSR解决了什么问题？有做过SSR吗？你是怎么做的？</a></li><li><a href="/fe/vue/structure.html" class="sidebar-link">面试官：说下你的vue项目的目录结构，如果是大型项目你该怎么划分结构和划分组件呢？</a></li><li><a href="/fe/vue/permission.html" class="sidebar-link">面试官：vue要做权限管理该怎么做？如果控制到按钮级别的权限怎么做？</a></li><li><a href="/fe/vue/cors.html" class="sidebar-link">面试官：Vue项目中你是如何解决跨域的呢？</a></li><li><a href="/fe/vue/404.html" class="sidebar-link">面试官：vue项目本地开发完成后部署到服务器后报404是什么原因呢？</a></li><li><a href="/fe/vue/error.html" class="sidebar-link">面试官：你是怎么处理vue项目中的错误的？</a></li><li><a href="/fe/vue/vue_router.html" class="sidebar-link">Vue Router</a></li><li><a href="/fe/vue/vue-debounce-throttle.html" class="sidebar-link">vue防抖调研</a></li></ul></section></li><li><section class="sidebar-group collapsable depth-0"><p class="sidebar-heading"><span>Vue3</span> <span class="arrow right"></span></p> <!----></section></li><li><section class="sidebar-group collapsable depth-0"><p class="sidebar-heading"><span>React</span> <span class="arrow right"></span></p> <!----></section></li><li><section class="sidebar-group collapsable depth-0"><p class="sidebar-heading"><span>Webpack</span> <span class="arrow right"></span></p> <!----></section></li><li><section class="sidebar-group collapsable depth-0"><p class="sidebar-heading"><span>Node.js</span> <span class="arrow right"></span></p> <!----></section></li><li><section class="sidebar-group collapsable depth-0"><p class="sidebar-heading"><span>性能优化</span> <span class="arrow right"></span></p> <!----></section></li><li><section class="sidebar-group collapsable depth-0"><p class="sidebar-heading"><span>手写代码</span> <span class="arrow right"></span></p> <!----></section></li></ul> </aside> <main class="page"> <div class="theme-default-content content__default"><h1 id="key的理解"><a href="#key的理解" class="header-anchor">#</a> Key的理解</h1> <p><img src="https://static.vue-js.com/bc6e9540-3f41-11eb-85f6-6fac77c0c9b3.png" alt=""></p> <p><code>key</code> 是给每一个 <code>vnode</code> 的唯一 id,可以依靠 <code>key</code>,更准确,更快的拿到 <code>oldVnode</code> 中对应的 <code>vnode</code> 节点，进行diff操作。</p> <p>diff算法的过程中，先会进行新旧节点的首尾交叉对比，当无法匹配的时候会用新节点的key与旧节点进行比对，然后找出差异.</p> <ul><li>准确：如果不加key,那么vue会选择复用节点(Vue的 <code>就地更新</code> 策略),导致之前节点的状态被保留下来,会产生一系列的bug.</li> <li>快速：key的唯一性可以被Map数据结构充分利用,相比于遍历查找的时间复杂度O(n),Map的时间复杂度仅仅为O(1).</li></ul> <h2 id="一、key是什么"><a href="#一、key是什么" class="header-anchor">#</a> 一、Key是什么</h2> <p>开始之前，我们先还原两个实际工作场景</p> <ol><li>当我们在使用<code>v-for</code>时，需要给单元加上<code>key</code></li></ol> <div class="language-js extra-class"><pre class="language-js"><code><span class="token operator">&lt;</span>ul<span class="token operator">&gt;</span>
    <span class="token operator">&lt;</span>li v<span class="token operator">-</span><span class="token keyword">for</span><span class="token operator">=</span><span class="token string">&quot;item in items&quot;</span> <span class="token operator">:</span>key<span class="token operator">=</span><span class="token string">&quot;item.id&quot;</span><span class="token operator">&gt;</span><span class="token operator">...</span><span class="token operator">&lt;</span><span class="token operator">/</span>li<span class="token operator">&gt;</span>
<span class="token operator">&lt;</span><span class="token operator">/</span>ul<span class="token operator">&gt;</span>
</code></pre></div><ol start="2"><li>用<code>+new Date()</code>生成的时间戳作为<code>key</code>，手动强制触发重新渲染</li></ol> <div class="language-js extra-class"><pre class="language-js"><code><span class="token operator">&lt;</span>Comp <span class="token operator">:</span>key<span class="token operator">=</span><span class="token string">&quot;+new Date()&quot;</span> <span class="token operator">/</span><span class="token operator">&gt;</span>
</code></pre></div><p>那么这背后的逻辑是什么，<code>key</code>的作用又是什么？</p> <p>一句话来讲</p> <blockquote><p>key是给每一个vnode的唯一id，也是diff的一种优化策略，可以根据key，更准确， 更快的找到对应的vnode节点</p></blockquote> <h3 id="场景背后的逻辑"><a href="#场景背后的逻辑" class="header-anchor">#</a> 场景背后的逻辑</h3> <p>当我们在使用<code>v-for</code>时，需要给单元加上<code>key</code></p> <ul><li><p>如果不用key，Vue会采用就地复地原则：最小化element的移动，并且会尝试尽最大程度在同适当的地方对相同类型的element，做patch或者reuse。</p></li> <li><p>如果使用了key，Vue会根据keys的顺序记录element，曾经拥有了key的element如果不再出现的话，会被直接remove或者destoryed</p></li></ul> <p>用<code>+new Date()</code>生成的时间戳作为<code>key</code>，手动强制触发重新渲染</p> <ul><li>当拥有新值的rerender作为key时，拥有了新key的Comp出现了，那么旧key Comp会被移除，新key Comp触发渲染</li></ul> <h2 id="二、设置key与不设置key区别"><a href="#二、设置key与不设置key区别" class="header-anchor">#</a> 二、设置key与不设置key区别</h2> <p>举个例子：</p> <p>创建一个实例，2秒后往<code>items</code>数组插入数据</p> <div class="language-html extra-class"><pre class="language-html"><code><span class="token tag"><span class="token tag"><span class="token punctuation">&lt;</span>body</span><span class="token punctuation">&gt;</span></span>
  <span class="token tag"><span class="token tag"><span class="token punctuation">&lt;</span>div</span> <span class="token attr-name">id</span><span class="token attr-value"><span class="token punctuation attr-equals">=</span><span class="token punctuation">&quot;</span>demo<span class="token punctuation">&quot;</span></span><span class="token punctuation">&gt;</span></span>
    <span class="token tag"><span class="token tag"><span class="token punctuation">&lt;</span>p</span> <span class="token attr-name">v-for</span><span class="token attr-value"><span class="token punctuation attr-equals">=</span><span class="token punctuation">&quot;</span>item in items<span class="token punctuation">&quot;</span></span> <span class="token attr-name">:key</span><span class="token attr-value"><span class="token punctuation attr-equals">=</span><span class="token punctuation">&quot;</span>item<span class="token punctuation">&quot;</span></span><span class="token punctuation">&gt;</span></span>{{item}}<span class="token tag"><span class="token tag"><span class="token punctuation">&lt;/</span>p</span><span class="token punctuation">&gt;</span></span>
  <span class="token tag"><span class="token tag"><span class="token punctuation">&lt;/</span>div</span><span class="token punctuation">&gt;</span></span>
  <span class="token tag"><span class="token tag"><span class="token punctuation">&lt;</span>script</span> <span class="token attr-name">src</span><span class="token attr-value"><span class="token punctuation attr-equals">=</span><span class="token punctuation">&quot;</span>../../dist/vue.js<span class="token punctuation">&quot;</span></span><span class="token punctuation">&gt;</span></span><span class="token script"></span><span class="token tag"><span class="token tag"><span class="token punctuation">&lt;/</span>script</span><span class="token punctuation">&gt;</span></span>
  <span class="token tag"><span class="token tag"><span class="token punctuation">&lt;</span>script</span><span class="token punctuation">&gt;</span></span><span class="token script"><span class="token language-javascript">
    <span class="token comment">// 创建实例</span>
    <span class="token keyword">const</span> app <span class="token operator">=</span> <span class="token keyword">new</span> <span class="token class-name">Vue</span><span class="token punctuation">(</span><span class="token punctuation">{</span>
      el<span class="token operator">:</span> <span class="token string">'#demo'</span><span class="token punctuation">,</span>
      data<span class="token operator">:</span> <span class="token punctuation">{</span> items<span class="token operator">:</span> <span class="token punctuation">[</span><span class="token string">'a'</span><span class="token punctuation">,</span> <span class="token string">'b'</span><span class="token punctuation">,</span> <span class="token string">'c'</span><span class="token punctuation">,</span> <span class="token string">'d'</span><span class="token punctuation">,</span> <span class="token string">'e'</span><span class="token punctuation">]</span> <span class="token punctuation">}</span><span class="token punctuation">,</span>
      <span class="token function">mounted</span> <span class="token punctuation">(</span><span class="token punctuation">)</span> <span class="token punctuation">{</span>
        <span class="token function">setTimeout</span><span class="token punctuation">(</span><span class="token punctuation">(</span><span class="token punctuation">)</span> <span class="token operator">=&gt;</span> <span class="token punctuation">{</span> 
          <span class="token keyword">this</span><span class="token punctuation">.</span>items<span class="token punctuation">.</span><span class="token function">splice</span><span class="token punctuation">(</span><span class="token number">2</span><span class="token punctuation">,</span> <span class="token number">0</span><span class="token punctuation">,</span> <span class="token string">'f'</span><span class="token punctuation">)</span>  <span class="token comment">// </span>
       <span class="token punctuation">}</span><span class="token punctuation">,</span> <span class="token number">2000</span><span class="token punctuation">)</span><span class="token punctuation">;</span>
     <span class="token punctuation">}</span><span class="token punctuation">,</span>
   <span class="token punctuation">}</span><span class="token punctuation">)</span><span class="token punctuation">;</span>
  </span></span><span class="token tag"><span class="token tag"><span class="token punctuation">&lt;/</span>script</span><span class="token punctuation">&gt;</span></span>
<span class="token tag"><span class="token tag"><span class="token punctuation">&lt;/</span>body</span><span class="token punctuation">&gt;</span></span>
</code></pre></div><p>在不使用<code>key</code>的情况，<code>vue</code>会进行这样的操作：</p> <p><img src="https://static.vue-js.com/c9da6790-3f41-11eb-85f6-6fac77c0c9b3.png" alt=""></p> <p>分析下整体流程：</p> <ul><li>比较A，A，相同类型的节点，进行<code>patch</code>，但数据相同，不发生<code>dom</code>操作</li> <li>比较B，B，相同类型的节点，进行<code>patch</code>，但数据相同，不发生<code>dom</code>操作</li> <li>比较C，F，相同类型的节点，进行<code>patch</code>，数据不同，发生<code>dom</code>操作</li> <li>比较D，C，相同类型的节点，进行<code>patch</code>，数据不同，发生<code>dom</code>操作</li> <li>比较E，D，相同类型的节点，进行<code>patch</code>，数据不同，发生<code>dom</code>操作</li> <li>循环结束，将E插入到<code>DOM</code>中</li></ul> <p>一共发生了3次更新，1次插入操作</p> <p>在使用<code>key</code>的情况：<code>vue</code>会进行这样的操作：</p> <ul><li>比较A，A，相同类型的节点，进行<code>patch</code>，但数据相同，不发生<code>dom</code>操作</li> <li>比较B，B，相同类型的节点，进行<code>patch</code>，但数据相同，不发生<code>dom</code>操作</li> <li>比较C，F，不相同类型的节点
<ul><li>比较E、E，相同类型的节点，进行<code>patch</code>，但数据相同，不发生<code>dom</code>操作</li></ul></li> <li>比较D、D，相同类型的节点，进行<code>patch</code>，但数据相同，不发生<code>dom</code>操作</li> <li>比较C、C，相同类型的节点，进行<code>patch</code>，但数据相同，不发生<code>dom</code>操作</li> <li>循环结束，将F插入到C之前</li></ul> <p>一共发生了0次更新，1次插入操作</p> <p>通过上面两个小例子，可见设置<code>key</code>能够大大减少对页面的<code>DOM</code>操作，提高了<code>diff</code>效率</p> <h3 id="设置key值一定能提高diff效率吗"><a href="#设置key值一定能提高diff效率吗" class="header-anchor">#</a> 设置key值一定能提高diff效率吗？</h3> <p>其实不然，文档中也明确表示</p> <blockquote><p>当 Vue.js 用 v-for 正在更新已渲染过的元素列表时，它默认用“就地复用”策略。如果数据项的顺序被改变，Vue 将不会移动 DOM 元素来匹配数据项的顺序， 而是简单复用此处每个元素，并且确保它在特定索引下显示已被渲染过的每个元素</p></blockquote> <p>这个默认的模式是高效的，但是只适用于不依赖子组件状态或临时 DOM 状态 (例如：表单输入值) 的列表渲染输出</p> <p>建议尽可能在使用 <code>v-for</code> 时提供 <code>key</code>，除非遍历输出的 DOM 内容非常简单，或者是刻意依赖默认行为以获取性能上的提升</p> <h2 id="三、原理分析"><a href="#三、原理分析" class="header-anchor">#</a> 三、原理分析</h2> <p>源码位置：core/vdom/patch.js</p> <p>这里判断是否为同一个<code>key</code>，首先判断的是<code>key</code>值是否相等如果没有设置<code>key</code>，那么<code>key</code>为<code>undefined</code>，这时候<code>undefined</code>是恒等于<code>undefined</code></p> <div class="language-js extra-class"><pre class="language-js"><code><span class="token keyword">function</span> <span class="token function">sameVnode</span> <span class="token punctuation">(</span><span class="token parameter">a<span class="token punctuation">,</span> b</span><span class="token punctuation">)</span> <span class="token punctuation">{</span>
    <span class="token keyword">return</span> <span class="token punctuation">(</span>
        a<span class="token punctuation">.</span>key <span class="token operator">===</span> b<span class="token punctuation">.</span>key <span class="token operator">&amp;&amp;</span> <span class="token punctuation">(</span>
            <span class="token punctuation">(</span>
                a<span class="token punctuation">.</span>tag <span class="token operator">===</span> b<span class="token punctuation">.</span>tag <span class="token operator">&amp;&amp;</span>
                a<span class="token punctuation">.</span>isComment <span class="token operator">===</span> b<span class="token punctuation">.</span>isComment <span class="token operator">&amp;&amp;</span>
                <span class="token function">isDef</span><span class="token punctuation">(</span>a<span class="token punctuation">.</span>data<span class="token punctuation">)</span> <span class="token operator">===</span> <span class="token function">isDef</span><span class="token punctuation">(</span>b<span class="token punctuation">.</span>data<span class="token punctuation">)</span> <span class="token operator">&amp;&amp;</span>
                <span class="token function">sameInputType</span><span class="token punctuation">(</span>a<span class="token punctuation">,</span> b<span class="token punctuation">)</span>
            <span class="token punctuation">)</span> <span class="token operator">||</span> <span class="token punctuation">(</span>
                <span class="token function">isTrue</span><span class="token punctuation">(</span>a<span class="token punctuation">.</span>isAsyncPlaceholder<span class="token punctuation">)</span> <span class="token operator">&amp;&amp;</span>
                a<span class="token punctuation">.</span>asyncFactory <span class="token operator">===</span> b<span class="token punctuation">.</span>asyncFactory <span class="token operator">&amp;&amp;</span>
                <span class="token function">isUndef</span><span class="token punctuation">(</span>b<span class="token punctuation">.</span>asyncFactory<span class="token punctuation">.</span>error<span class="token punctuation">)</span>
            <span class="token punctuation">)</span>
        <span class="token punctuation">)</span>
    <span class="token punctuation">)</span>
<span class="token punctuation">}</span>
</code></pre></div><p><code>updateChildren</code>方法中会对新旧<code>vnode</code>进行<code>diff</code>，然后将比对出的结果用来更新真实的<code>DOM</code></p> <div class="language-js extra-class"><pre class="language-js"><code><span class="token keyword">function</span> <span class="token function">updateChildren</span> <span class="token punctuation">(</span><span class="token parameter">parentElm<span class="token punctuation">,</span> oldCh<span class="token punctuation">,</span> newCh<span class="token punctuation">,</span> insertedVnodeQueue<span class="token punctuation">,</span> removeOnly</span><span class="token punctuation">)</span> <span class="token punctuation">{</span>
    <span class="token operator">...</span>
    <span class="token keyword">while</span> <span class="token punctuation">(</span>oldStartIdx <span class="token operator">&lt;=</span> oldEndIdx <span class="token operator">&amp;&amp;</span> newStartIdx <span class="token operator">&lt;=</span> newEndIdx<span class="token punctuation">)</span> <span class="token punctuation">{</span>
        <span class="token keyword">if</span> <span class="token punctuation">(</span><span class="token function">isUndef</span><span class="token punctuation">(</span>oldStartVnode<span class="token punctuation">)</span><span class="token punctuation">)</span> <span class="token punctuation">{</span>
            <span class="token operator">...</span>
        <span class="token punctuation">}</span> <span class="token keyword">else</span> <span class="token keyword">if</span> <span class="token punctuation">(</span><span class="token function">isUndef</span><span class="token punctuation">(</span>oldEndVnode<span class="token punctuation">)</span><span class="token punctuation">)</span> <span class="token punctuation">{</span>
            <span class="token operator">...</span>
        <span class="token punctuation">}</span> <span class="token keyword">else</span> <span class="token keyword">if</span> <span class="token punctuation">(</span><span class="token function">sameVnode</span><span class="token punctuation">(</span>oldStartVnode<span class="token punctuation">,</span> newStartVnode<span class="token punctuation">)</span><span class="token punctuation">)</span> <span class="token punctuation">{</span>
            <span class="token operator">...</span>
        <span class="token punctuation">}</span> <span class="token keyword">else</span> <span class="token keyword">if</span> <span class="token punctuation">(</span><span class="token function">sameVnode</span><span class="token punctuation">(</span>oldEndVnode<span class="token punctuation">,</span> newEndVnode<span class="token punctuation">)</span><span class="token punctuation">)</span> <span class="token punctuation">{</span>
            <span class="token operator">...</span>
        <span class="token punctuation">}</span> <span class="token keyword">else</span> <span class="token keyword">if</span> <span class="token punctuation">(</span><span class="token function">sameVnode</span><span class="token punctuation">(</span>oldStartVnode<span class="token punctuation">,</span> newEndVnode<span class="token punctuation">)</span><span class="token punctuation">)</span> <span class="token punctuation">{</span> <span class="token comment">// Vnode moved right</span>
            <span class="token operator">...</span>
        <span class="token punctuation">}</span> <span class="token keyword">else</span> <span class="token keyword">if</span> <span class="token punctuation">(</span><span class="token function">sameVnode</span><span class="token punctuation">(</span>oldEndVnode<span class="token punctuation">,</span> newStartVnode<span class="token punctuation">)</span><span class="token punctuation">)</span> <span class="token punctuation">{</span> <span class="token comment">// Vnode moved left</span>
            <span class="token operator">...</span>
        <span class="token punctuation">}</span> <span class="token keyword">else</span> <span class="token punctuation">{</span>
            <span class="token keyword">if</span> <span class="token punctuation">(</span><span class="token function">isUndef</span><span class="token punctuation">(</span>oldKeyToIdx<span class="token punctuation">)</span><span class="token punctuation">)</span> oldKeyToIdx <span class="token operator">=</span> <span class="token function">createKeyToOldIdx</span><span class="token punctuation">(</span>oldCh<span class="token punctuation">,</span> oldStartIdx<span class="token punctuation">,</span> oldEndIdx<span class="token punctuation">)</span>
            idxInOld <span class="token operator">=</span> <span class="token function">isDef</span><span class="token punctuation">(</span>newStartVnode<span class="token punctuation">.</span>key<span class="token punctuation">)</span>
                <span class="token operator">?</span> oldKeyToIdx<span class="token punctuation">[</span>newStartVnode<span class="token punctuation">.</span>key<span class="token punctuation">]</span>
                <span class="token operator">:</span> <span class="token function">findIdxInOld</span><span class="token punctuation">(</span>newStartVnode<span class="token punctuation">,</span> oldCh<span class="token punctuation">,</span> oldStartIdx<span class="token punctuation">,</span> oldEndIdx<span class="token punctuation">)</span>
            <span class="token keyword">if</span> <span class="token punctuation">(</span><span class="token function">isUndef</span><span class="token punctuation">(</span>idxInOld<span class="token punctuation">)</span><span class="token punctuation">)</span> <span class="token punctuation">{</span> <span class="token comment">// New element</span>
                <span class="token function">createElm</span><span class="token punctuation">(</span>newStartVnode<span class="token punctuation">,</span> insertedVnodeQueue<span class="token punctuation">,</span> parentElm<span class="token punctuation">,</span> oldStartVnode<span class="token punctuation">.</span>elm<span class="token punctuation">,</span> <span class="token boolean">false</span><span class="token punctuation">,</span> newCh<span class="token punctuation">,</span> newStartIdx<span class="token punctuation">)</span>
            <span class="token punctuation">}</span> <span class="token keyword">else</span> <span class="token punctuation">{</span>
                vnodeToMove <span class="token operator">=</span> oldCh<span class="token punctuation">[</span>idxInOld<span class="token punctuation">]</span>
                <span class="token keyword">if</span> <span class="token punctuation">(</span><span class="token function">sameVnode</span><span class="token punctuation">(</span>vnodeToMove<span class="token punctuation">,</span> newStartVnode<span class="token punctuation">)</span><span class="token punctuation">)</span> <span class="token punctuation">{</span>
                    <span class="token function">patchVnode</span><span class="token punctuation">(</span>vnodeToMove<span class="token punctuation">,</span> newStartVnode<span class="token punctuation">,</span> insertedVnodeQueue<span class="token punctuation">,</span> newCh<span class="token punctuation">,</span> newStartIdx<span class="token punctuation">)</span>
                    oldCh<span class="token punctuation">[</span>idxInOld<span class="token punctuation">]</span> <span class="token operator">=</span> <span class="token keyword">undefined</span>
                    canMove <span class="token operator">&amp;&amp;</span> nodeOps<span class="token punctuation">.</span><span class="token function">insertBefore</span><span class="token punctuation">(</span>parentElm<span class="token punctuation">,</span> vnodeToMove<span class="token punctuation">.</span>elm<span class="token punctuation">,</span> oldStartVnode<span class="token punctuation">.</span>elm<span class="token punctuation">)</span>
                <span class="token punctuation">}</span> <span class="token keyword">else</span> <span class="token punctuation">{</span>
                    <span class="token comment">// same key but different element. treat as new element</span>
                    <span class="token function">createElm</span><span class="token punctuation">(</span>newStartVnode<span class="token punctuation">,</span> insertedVnodeQueue<span class="token punctuation">,</span> parentElm<span class="token punctuation">,</span> oldStartVnode<span class="token punctuation">.</span>elm<span class="token punctuation">,</span> <span class="token boolean">false</span><span class="token punctuation">,</span> newCh<span class="token punctuation">,</span> newStartIdx<span class="token punctuation">)</span>
                <span class="token punctuation">}</span>
            <span class="token punctuation">}</span>
            newStartVnode <span class="token operator">=</span> newCh<span class="token punctuation">[</span><span class="token operator">++</span>newStartIdx<span class="token punctuation">]</span>
        <span class="token punctuation">}</span>
    <span class="token punctuation">}</span>
    <span class="token operator">...</span>
<span class="token punctuation">}</span>
</code></pre></div><h2 id="参考文献"><a href="#参考文献" class="header-anchor">#</a> 参考文献</h2> <ul><li><a href="https://juejin.cn/post/6844903826693029895" target="_blank" rel="noopener noreferrer">https://juejin.cn/post/6844903826693029895<span><svg xmlns="http://www.w3.org/2000/svg" aria-hidden="true" focusable="false" x="0px" y="0px" viewBox="0 0 100 100" width="15" height="15" class="icon outbound"><path fill="currentColor" d="M18.8,85.1h56l0,0c2.2,0,4-1.8,4-4v-32h-8v28h-48v-48h28v-8h-32l0,0c-2.2,0-4,1.8-4,4v56C14.8,83.3,16.6,85.1,18.8,85.1z"></path> <polygon fill="currentColor" points="45.7,48.7 51.3,54.3 77.2,28.5 77.2,37.2 85.2,37.2 85.2,14.9 62.8,14.9 62.8,22.9 71.5,22.9"></polygon></svg> <span class="sr-only">(opens new window)</span></span></a></li> <li><a href="https://juejin.cn/post/6844903985397104648" target="_blank" rel="noopener noreferrer">https://juejin.cn/post/6844903985397104648<span><svg xmlns="http://www.w3.org/2000/svg" aria-hidden="true" focusable="false" x="0px" y="0px" viewBox="0 0 100 100" width="15" height="15" class="icon outbound"><path fill="currentColor" d="M18.8,85.1h56l0,0c2.2,0,4-1.8,4-4v-32h-8v28h-48v-48h28v-8h-32l0,0c-2.2,0-4,1.8-4,4v56C14.8,83.3,16.6,85.1,18.8,85.1z"></path> <polygon fill="currentColor" points="45.7,48.7 51.3,54.3 77.2,28.5 77.2,37.2 85.2,37.2 85.2,14.9 62.8,14.9 62.8,22.9 71.5,22.9"></polygon></svg> <span class="sr-only">(opens new window)</span></span></a></li> <li><a href="https://vue3js.cn/docs/zh" target="_blank" rel="noopener noreferrer">https://vue3js.cn/docs/zh<span><svg xmlns="http://www.w3.org/2000/svg" aria-hidden="true" focusable="false" x="0px" y="0px" viewBox="0 0 100 100" width="15" height="15" class="icon outbound"><path fill="currentColor" d="M18.8,85.1h56l0,0c2.2,0,4-1.8,4-4v-32h-8v28h-48v-48h28v-8h-32l0,0c-2.2,0-4,1.8-4,4v56C14.8,83.3,16.6,85.1,18.8,85.1z"></path> <polygon fill="currentColor" points="45.7,48.7 51.3,54.3 77.2,28.5 77.2,37.2 85.2,37.2 85.2,14.9 62.8,14.9 62.8,22.9 71.5,22.9"></polygon></svg> <span class="sr-only">(opens new window)</span></span></a></li></ul></div> <footer class="page-edit"><!----> <div class="last-updated"><span class="prefix">更新时间:</span> <span class="time">12/14/2021, 10:12:35 AM</span></div></footer> <div class="page-nav"><p class="inner"><span class="prev">
      ←
      <a href="/fe/vue/observable.html" class="prev">
        面试官：Vue.observable你有了解过吗？说说看
      </a></span> <span class="next"><a href="/fe/vue/keepalive.html">
        面试官：说说你对keep-alive的理解是什么？
      </a>
      →
    </span></p></div> </main></div><div class="global-ui"><!----></div></div>
    <script src="/assets/js/app.bf44e39b.js" defer></script><script src="/assets/js/2.db7a59af.js" defer></script><script src="/assets/js/222.51d8a12c.js" defer></script>
  </body>
</html>
